A new approach to the synthesis of lysophosphatidylcholines and related derivatives

Article abstract of DOI:10.1016/S0040-4039(03)01419-9

A new stereospecific synthesis of lysophosphatidylcholines is reported. The sequence relies on orthogonal protection of hydroxyl groups derived from glyceric acid, using fluorenylmethylcarbonate versus tetrahydropyranyl ether functions, that allow regiospecific introduction of substituents to obtain the target phospholipid compound.

Full text of DOI:10.1016/S0040-4039(03)01419-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 5875–5877
A new approach to the synthesis of lysophosphatidylcholines and
related derivatives
Niloufar Bibak and Joseph Hajdu*
Department of Chemistry, California State University, Northridge, CA 91330-8262, USA
Received 30 April 2003; revised 2 June 2003; accepted 3 June 2003
Abstract—A new stereospecific synthesis of lysophosphatidylcholines is reported. The sequence relies on orthogonal protection of
hydroxyl groups derived from glyceric acid, using fluorenylmethylcarbonate versus tetrahydropyranyl ether functions, that allow
regiospecific introduction of substituents to obtain the target phospholipid compound.
©
2003 Elsevier Ltd. All rights reserved.
Development of new synthetic methods for the prepara-
tion of biologically active phospholipid derivatives is
one of the most timely problems in membrane-chem-
efficient synthetic methods for preparation of struc-
turally variable lysophospholipid derivatives.
1
istry today. The compounds are required for structural
To date preparation of lysophospholipids has mainly
2
10
and dynamic studies of biomembranes and membrane-
relied on semisynthesis, which imposes significant lim-
3
bound enzymes to establish structure–activity relation-
itations on the scope and the scale of the compounds
that can be prepared. We now describe a new scheme
for the synthesis of lysophosphatidylcholines 1, provid-
ing a general method that should be applicable to the
preparation of saturated as well as unsaturated com-
pounds, including functionalized derivatives with spec-
troscopically active reporter groups as structural and
mechanistic probes for biophysical and cell-biological
studies.
ships with respect to phospholipid–phospholipid and
4
phospholipid–protein
interactions.
Specifically,
lysophosphatidylcholine 1 belongs to an important
Reduction of 2,3-O-isopropylidene-
L
-methyl glycerate 2
with LiBH in ether yielded the corresponding alcohol
4
class of phospholipid compounds that are not only
substrates and products of phospholipid metabolizing
(
95%) which was acylated with palmitic acid/DCC in
the presence of catalytic amount of 4-(dimethyl-
amino)pyridine (DMAP) in chloroform at rt overnight.
The resulting ester 3 was purified by silica gel chro-
matography (hexane–ethyl acetate 2:3) and isolated in
95% yield. Acid-catalyzed deprotection of 3 with 0.4N
HCl in 90% aq. dioxane at rt for 2 h, followed by
freeze-drying and chromatography yielded pure 1-pal-
mitoyl-sn-glycerol 4 (84%).
5
enzymes, but also have a wide range of physiological
6
–9
roles in their own right. Lysophospholipids have long
7
been known to function as immunomodulators, and
have recently been recognized as highly potent extracel-
lular regulators of cell growth, differentiation, and
8
related activities through G-protein coupled receptors.
Elucidation of the mechanistic details involved in the
enzymological, cell-biological and membrane-biophysi-
cal activities of lysophosphatidylcholines remains to be
accomplished, and it greatly depends on availability of
Regiospecific monoacylation of compound 4 was
accomplished using twofold molar excess of diol 4 in
reaction with FMOC-chloroformate in the presence of
1
equiv. DMAP in methylene chloride at −10°C for 30
min. The product 5 was chromatographed on silica gel
hexane–ethyl acetate 1:3) to afford analytically pure
(
Keywords: lysophosphatidylcholine synthesis; methyl glycerate;
orthogonal O-protection.
1
FMOC-carbonate 5 in 58% yield. Absence of the H
NMR signal in the l 5.00–5.09 region clearly indicated
that the secondary hydroxyl group of the compound 5
*
Corresponding author. Tel.: (818) 677-3377; fax: (818) 677-2912;
e-mail: joseph.hajdu@csun.edu
0
040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01419-9

5
876
N. Bibak, J. Hajdu / Tetrahedron Letters 44 (2003) 5875–5877
1
1
remained intact in the isolated product.
Tetra-
Since lysophosphatidylcholines also serve as synthetic
precursors of diacyl glycerophosphocholines we used
the product 1% that became available from Scheme 1 to
prepare the corresponding phosphatidylcholine via
DMAP-catalyzed acyl transfer reaction from a p-nitro-
phenyl ester to the sn-2-hydroxyl group of compound 1%
(Eq. (1)).
hydropyranylation of the sn-2-hydroxyl group with
pyridinium p-toluenesulfonate catalysis gave compound
, isolated in 86% yield as a colorless oil. Selective
6
cleavage of the FMOC-carbonate function was
achieved using 10% piperidine solution in CH Cl at rt
2
2
for 1 h. Compound 7 was isolated by chromatography,
followed by freeze-drying from benzene as a hygro-
scopic white solid (87%).
Thus, reaction of 1-palmitoyl-sn-glycerophospho-
choline 1% with fourfold excess of p-nitrophenyl ester/
Phosphorylation of the functionalized glycerol 7 at the
sn-3 position was carried out with 2-chloro-2-oxo-1,3,2-
DMAP in anhydrous CHCl , sonicated at 40°C for 48
3
h, afforded the corresponding diacyl compound 9 as a
single phospholipid. The product 9 was purified by first
1b
dioxaphospholane/triethylamine in dry benzene. The
phosphorylated intermediate was treated with anhy-
drous trimethylamine in acetonitrile at 65°C (in a pres-
sure bottle) for 24 h to afford the crude phospholipid 8
that separated from the reaction mixture on cooling.
The product 8 was purified by silica gel chromatogra-
+
passing it through a Bio-Rad AG 50-X (H ) cation
exchange resin (to remove the catalyst), followed by
silica gel chromatography (chloroform–methanol–water
65:25:4) to give pure 9 in 62% yield.
phy
(chloroform–methanol–water
65:25:4)
and
We believe that the active ester/DMAP method for
acylation of lysophospholipids provides an improved
alternative to the traditional acylation methods used to
introduce the sn-2-substituent to obtain structurally
well-defined phosphatidylcholines. Specifically, in con-
trast to the widely used fatty acid/DCC/DMAP or fatty
obtained in 61% yield.
Compound 8 was subjected to acid hydrolysis in 0.15N
HCl in dioxane–water (1:1), freeze-dried, and chro-
matographed on Sephadex LH-20 using chloroform–
methanol (1:1) to give the target compound
-palmitoyl-sn-glycerophosphocholine 1% in 98% yield.
Evidence that no acid-catalyzed acyl migration
occurred during deprotection step came from both the
H NMR and P NMR spectra of the product 1%.
Specifically, the proton NMR spectrum of compound 1%
shows base-line absorption in the l 5.00–5.09 range,
and the phosphorus NMR shows a single peak at l
10
acid anhydride/DMAP methods, the use of an active
ester acyl donor generates p-nitrophenolate as
byproduct, which is several orders of magnitude less
basic than the corresponding carboxylate ion formed in
1
1
31
12
the reaction mixture. Since base-catalyzed acyl migra-
tion and racemization have been reported to be signifi-
11
10
cant concerns in the reaction, a weaker base present in
the reaction mixture may improve both regio- and
stereospecificity in obtaining the products.
5
0
.12 while no second peak is apparent in the spectrum.
Scheme 1.

N. Bibak, J. Hajdu / Tetrahedron Letters 44 (2003) 5875–5877
5877
(1)
In conclusion, the synthesis here reported provides a
rapid and efficient method for preparation of lysophos-
phatidylcholines and their related diacyl phospholipid
derivatives. The strength of the synthesis is in its flexi-
bility with respect to the substituents that can be intro-
9. Goetzl, E. J. Prostaglandins Other Lipids Med. 2001, 64,
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10. Bittman, R. In Phospholipid Handbook; Cevc, G., Ed.;
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phospholipid analogues with desired target structures
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4
for biological and physicochemical studies.
6192.
1
3. We have obtained preliminary evidence that the same
series of reactions can also be carried out using a series of
substituted fatty acid derivatives. Along these lines, car-
boxylic acids functionalized at the chain terminal position
with fluorescent reporter groups such as coumarin-343,
and metal binding tetraazacyclododecyl groups have been
incorporated into the synthetic phospholipid compounds.
Acknowledgements
This work was supported by the National Institute of
Health, including grants GM41452, S06 GM/HD48680
and T34 GM08395.
1
13
1
4. All new compounds were characterized by IR, H,
C
NMR, HR MS and elemental analysis. Selected data: 5:
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31
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3
15
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8
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